Method of synthesis of anhydrous thorium(IV) complexes

ABSTRACT

Method of producing anhydrous thorium(IV) tetrahalide complexes, utilizing Th(NO 3 ) 4 (H 2 O) x , where x is at least 4, as a reagent; method of producing thorium-containing complexes utilizing ThCl 4 (DME) 2  as a precursor; method of producing purified ThCl 4 (ligand) x  compounds, where x is from 2 to 9; and novel compounds having the structures:

STATEMENT OF FEDERAL RIGHTS

The United States government has rights in this invention pursuant toContract No. DE-AC52-06NA25396 between the United States Department ofEnergy and Los Alamos National Security, LLC for the operation of LosAlamos National Laboratory.

FIELD OF THE INVENTION

The present invention relates to methods of synthesis of anhydrousthorium(IV) tetrahalide complexes, including ThCl₄(DME)₂,ThCl₄(1,4-dioxane)₂, and ThCl₄(THF)_(x), using Th(NO₃)₄(H₂O)_(x) as aprecursor, in high yield and under comparatively mild reactionconditions.

BACKGROUND OF THE INVENTION

Anhydrous halide complexes are key starting materials in the synthesisof transition metal, lanthanide and actinide complexes. For non-aqueousthorium chemistry, ThBr₄(THF)₄ and ThCl₄ have been the most commonlyused precursors, but their syntheses suffer from several inconvenientdrawbacks, which have, in turn, greatly hampered progress in thoriumresearch. For example, the synthesis of ThBr₄(THF)₄ requires thorium(0)metal, a material which is both expensive and available at only a smallnumber of institutions. Furthermore, synthesis of thorium(0) metal ishighly dependent on the type of thorium metal used (e.g., turnings,powder or chips) and the complex is thermally sensitive withring-opening and subsequent polymerization of THF being a problem. Thesynthetic procedures for ThCl₄ require special equipment and moredangerous protocols that involve elevated temperatures (300-500° C.).For example, one method involves reacting thorium dioxide or thoria(ThO₂) with CCl₄ vapor at 450-500° C. for several days, while anotherrequires heating thorium metal with NH₄Cl at 300° C. for 30 h toinitially generate (NH₄)₂ThCl₆, which is then heated at 350° C. underhigh vacuum to ultimately give ThCl₄.

The increasing use of thorium in catalysis and materials science,coupled with the growing interest in developing aproliferation-resistant thorium nuclear fuel cycle, creates a need forstraightforward access to anhydrous thorium(IV) starting materials.

SUMMARY OF THE INVENTION

The present invention meets the aforementioned need by describing novelmethods of safer and more economically viable thorium(IV) halidesyntheses, which share none of the disadvantages of previously availablemethods, e.g., are performed at lower temperatures, require shorterreaction periods and reproducibly result in high yields. The presentinvention utilizes thorium nitrate, Th(NO₃)₄(H₂O)_(x), where x is atleast 4, as a safe and economically viable starting material for thesynthesis of thorium(IV) chloride hydrates. Anhydrous HCl and Me₃SiClserve as effective drying reagents in reactions that produce ThCl₄(DME)₂and ThCl₄(1,4-dioxane)₂. ThCl₄(DME)₂ may be used as a starting materialin reactions to produce a number of useful products, as depicted inFIG. 1. Finally, ThCl₄(1,4-dioxane)₂ may be easily converted to novelthorium complexes ThCl₄(THF)_(x) in good yield and under mild reactionconditions.

The following describe some non-limiting embodiments of the presentinvention.

According to one embodiment of the present invention, a method ofproducing anhydrous thorium(IV) tetrahalide complexes is provided,comprising providing Th(NO₃)₄(H₂O)_(x), where x is at least 4; reactingsaid Th(NO₃)₄(H₂O)₅ with a halide-containing strong acid to produceThX₄(H₂O)₄, wherein X is a halide selected from the group consisting ofbromide, chloride, iodide, and combinations thereof; and, drying theThX₄(H₂O)₄ with Me₃SiCl or a mixture of anhydrous HCl and Me₃SiCl in asuitable solvent to produce a ThX₄-ligand complex.

According to another embodiment of the present invention, a method ofproducing thorium-containing complexes is provided, comprising providingThCl₄(dimethoxyethane)₂; and, reacting the ThCl₄(dimethoxyethane)₂ witha suitable reagent to produce thorium(IV) complexes comprisingthorium(IV)-oxygen bonds, thorium(IV)-nitrogen bonds, thorium(IV)-halidebonds, thorium(IV)-carbon bonds, and combinations thereof.

According to yet another embodiment of the present invention, a methodof producing purified ThCl₄(ligand)_(x) compounds, where x=from 2 to 9,is provided, comprising providing ThCl₄(1,4-dioxane)₂; and, reacting theThCl₄(1,4-dioxane)₂ with a suitable ligand donor to produceThCl₄(ligand)_(x).

According to yet another embodiment of the present invention, a compoundis provided comprising:

According to yet another embodiment of the present invention, a compoundis provided comprising:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts non-limiting examples of reactions and products ofThCl₄(DME)₂. Reagents and conditions: (i) 3 equiv. Ph₃P═O, THF, 100%yield; (ii) excess TMEDA, THF, 100% yield; (iii) excess Me₃SiBr,toluene, 24 h, 100% yield; (iv) 4 equiv. KOAr (Ar=2,6-^(t)Bu₂-C₆H₃),THF, 99% yield; (v) 4 equiv. Na[N(SiMe₃)₂], toluene, reflux, 12 h, 93%yield; (vi) 2 equiv. (C₅Me₅)MgCl.THF, toluene, reflux, 24 h, 88% yield.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to methods of producing a variety ofthorium(IV) containing complexes. Herein, the terms complexes, adductsand compounds are used interchangeably.

Aspects of the present invention are described by Thibault Cantat, BrianL. Scott and Jaqueline L. Kiplinger in Chem. Commun., 2010, 46, pp.919-921, incorporated herein by reference in its entirety.

One aspect of the present invention describes a method of producinganhydrous thorium(IV) tetrahalide complexes. The method usesTh(NO₃)₄(H₂O)₅ as a starting material, which is allowed to react with ahalide-containing strong acid to produce ThX₄(H₂O)₄. In addition tothorium, other actinide nitrate compounds may be used as startingmaterials, including uranium, neptunium and plutonium nitrates. It alsoshould be noted that the number of (H₂O) ligands in the startingmaterial may vary. For example, Th(NO₃)₄(H₂O)_(x) may be used, where xis at least 4, and in theory, has no upper limit. The halide in thestrong acid may be bromide, chloride and/or iodide, and in oneembodiment is chloride. Fluoride-containing acids are not consideredsuitable for use in the present invention, due to high reactivity andsafety concerns. Upon formation of the ThX₄(H₂O)₄, the product is driedwith a suitable drying agent in the presence of a solvent. Examples ofsuitable drying agents include, but are not limited to, Me₃SiCl(chlorotrimethylsilane), Me₃SiBr (bromotrimethylsilane), Me₃SiI(iodotrimethylsilane), thionyl chloride (SOCl₂), and phosgene (COCl₂),to name a few. However, Me₃SiCl has several advantages, such as notrequiring extensive purification prior to use, shorter reaction times,lower temperatures, and fewer safety concerns. Thus, in one embodiment,the drying agent is Me₃SiCl. It is believed that the present inventiondescribes for the first time that the combination of a strong acid suchas HCl and Me₃SiCl has been used to successfully dry wet compounds toproduce anhydrous compounds.

The type of solvent determines which ThX₄-ligand complex is formed.Non-limiting examples of solvents that may be used includedimethoxyethane (DME), dioxanes (including 1,4-dioxane), pyridines,amines, ethers (oxygen, sulfur, selenium, tellurium), nitrites,isonitriles, ketones, aldehydes, phopshines, phosphine oxides, phosphinesulfides, phosphine selenides, phoephine tellurides, pyridine N-oxides,thiocarbamates, N-heterocyclic carbenes, thiols, alcohols, selenols,tellurols, isocyanates, thioisocyanates, heterocumulenes, sulfoxides,furans, and combinations thereof. In one embodiment, the solvent isselected from the group consisting of dimethoxyethane (DME),tetrahydrofuran (THF), 1,4-dioxane, and combinations thereof. When DMEis used as a solvent, the ThX₄-ligand complex formed isThCl₄(dimethoxyethane)₂, which has the following structure:

When a dioxane such as 1,4-dioxane is used, the novel compoundThCl₄(1,4-dioxane)₂ is, formed, which is useful, for among other things,as a reagent for producing heretofore difficult or impossible to produceThCl₄ complexes. ThCl₄(1,4-dioxane)₂ has the following structure:

The reactions are performed at a temperature of 100° C. or less, for aperiod of about 12 hours or less. By means of example only, reaction (1)may be performed for about 6 hours, and reaction (2) may be performedfor about 12 hours (see Example 1). The % yield, defined as the (mass ofthe product recovered from the reaction/the theoretical maximum mass ofobtainable product)×100, is at least 90%.

Another aspect of the present invention provides a method of producing avariety of thorium-containing complexes, which prior to the presentinvention, had been extremely difficult to produce in purified form andin useful quantities (on the order of grams). When ThCl₄(DME)₂ isallowed to undergo a reaction with a variety of reagents, thorium(IV)complexes are produced which contain thorium(IV)-oxygen bonds,thorium(IV)-nitrogen bonds, thorium(IV)-halide bonds and/orthorium(IV)-carbon bonds, which are critical for developing routes tothorium-oxides, thorium-nitrides, thorium-carbides and sol-gel sciencefor nuclear materials storage, processing, and fuel. These homogeneousthorium complexes will also be invaluable for grafting thorium ontosolid supports for industrial or large scale applications and closingthe thorium fuel cycle. FIG. 1 depicts the various thorium(IV) complexesthat are produced, including thorium(IV) halide complexes, such asThBr₄(dimethoxyethane)₂, ThCl₄(N,N′-tetramethylenediamine)₂, andThCl₄(O═PPh₃)₃; thorium(IV) alkoxide complexes, such asTh(O-2,6-^(t)Bu₂-C₆H₃)₄; thorium(IV) amide complexes, such as[(Me₃Si)₂N]₂Th[κ²-(C,N)—CH₂Si(CH₃)₂N(SiMe₃)]; and thorium(IV)organometallic complexes, such as (C₅Me₅)₂ThCl₂ and[(Me₃Si)₂N]₂Th[κ²-(C,N)—0-11Si(CH₃)₂N(SiMe₃)]. Suitable reagentsinclude, but are not limited to, triphenylphosphine oxide,N,N′-tetramethylethylenediamine, bromotrimethylsilane,iodotrimethylsilane, potassium 2,6-di-tert-butylphenoxide, sodiumhexamethyldisilazide, (C₅Me₅)MgCl.THF, and combinations thereof. Thecomplexes typically are produced in a yield of at least 80%, and have apurity of at least 90%, alternatively of at least 95%, and alternativelyof at least 99%.

Another aspect of the present invention provides a method for producingpurified ThCl₄(ligand)_(x), complexes, wherein x is from 2 to 9, andalternatively from 3 to 4, and alternatively is 3.5. In this method,ThCl₄(1,4-dioxane)₂ is used as a starting material and allowed to reactwith a suitable ligand donor. One non-limiting example of a suitabledonor is tetrahydrofuran (THF), which results in ThCl₄(THF)_(3.5),having the following structure:

The significance of this aspect lies in the fact that ThCl₄(THF)₁₅ isextremely useful as a starting material in non-aqueous thoriumcomplexes, and prior to this work has not been possible to produce inuseful, purified quantities (e.g., in gram quantities). As has beendescribed previously in the literature, coordination of THF to anelectrophilic actinide metal center leads to ring-opening followingnucleophilic attack from another molecule of THF, which leads to THFpolymerization. This results in essentially no yield of ThCl₄-THFcomplexes, and any that is produced cannot be separated from thepolymeric matrix. Conversion of ThCl₄(1,4-dioxane)₂ to ThCl₄(THF)_(3.5)occurs in a yield of at least 90%, and may be greater than 99%.

Finally, both ThCl₄(1,4-dioxane)₂ and ThCl₄(THF)_(3.5) can be convertedto ThCl₄(DME)₂Thus, both are useful precursors for the synthesis ofthorium halide, alkoxide, amide and organometallic compounds.

EXAMPLES General Synthetic Considerations

Unless otherwise noted, all reactions and manipulations were performedat 20° C. in a recirculating Vacuum Atmospheres NEXUS Model inertatmosphere (N₂) drybox equipped with a 40CFM Dual Purifier NI-Train.Glassware was dried overnight at 150° C. before use. All NMR spectrawere obtained using a Bruker Avance 300 MHz spectrometer. Chemicalshifts for ¹H and ¹³C {¹H} NMR spectra were referenced to solventimpurities. Elemental analyses (C, H, Cl and Th) were performed atColumbia Analytical Services in Tucson and Phoenix, Ariz. X-ray datawere collected using a Bruker APEX2 diffractometer. Structural solutionand refinement was achieved using the SHELXL program suite, i.e.,Bruker, APEX2 1.08, APEX2 Data Collection Software; Bruker AnalyticalX-ray Systems: Madison, Wis., 2003; Bruker, SAINT+ 7.06, IntegrationSoftware; Bruker Analytical X-ray Systems: Madison, Wis., 2001;Sheldrick, G. M. SADABS 2.03, Program for Adsorption Correction;University of Göttingen: Göttingen, Germany, 2001; Sheldrick, G. M.SHELXS-97 and SHELXL-97, Structure Solution and Refinement Package;Universitiy of Göttingen: Göttingen, Germany, 1997; Bruker, SHELXTL6.10, Molecular Graphics and Publication Software Package; BrukerAnalytical X-ray Systems: Madison, Wis., 2000. Details regarding datacollection are provided in the CIF files which can be found at DOI:10.1039/b923558b.

Unless otherwise noted, reagents were purchased from commercialsuppliers and used without further purification. Celite (Aldrich),alumina (Brockman I, Aldrich) and 4 Å molecular sieves (Aldrich) weredried under dynamic vacuum at 250° C. for 48 h prior to use. Allsolvents (Aldrich) were purchased anhydrous, dried over KH for 24 h,passed through a column of activated alumina, and stored over activated4 Å molecular sieves prior to use. Benzene-d₆ (Aldrich) andtetrahydrofuran-d₈ (Cambridge Isotope Laboratories) were purified bystorage over activated 4 Å molecular sieves or sodium metal prior touse. Th(NO₃)₄(H₂O)₅ was purchased from Merck. Triphenylphosphine oxide,Na[N(SiMe₃)₂], Me₃SiCl, Me₃SiBr, concentrated HCl (37 wt. % in H₂O, 12M), HCl/diethyl ether (2.0M) were purchased from Aldrich.(C₅Me₅)MgCl.THF and K(O-2,6-^(t)Bu₂-C₆H₃) were prepared according toliterature procedures. Caution: Natural thorium (primary isotope in') isa weak alpha-emitter (4.012 MeV) with a half-life of 1.41×10¹⁰ years;manipulations and reactions should be carried out in monitored fumehoods or in an inert atmosphere drybox in a radiation laboratoryequipped with alpha- and beta-counting equipment.

Example 1

As shown in eqn (1), quantitative conversion of Th(NO₃)₄(H₂O)₅ into thethorium(IV) chloride tetrahydrate complex ThCl₄(H₂O)₄ was achieved byrefluxing Th(NO₃)₄(H₂O)₅ in concentrated aqueous HCl (12 M) solution.ThCl₄(H₂O)₄ is a white solid, and is insoluble in hydrocarbons butsoluble in tetrahydrofuran (THF), dimethoxyethane (DME) and 1,4-dioxane.Confirmation of a tetrahydrate form was determined by elementalanalysis, as well as recrystallization from THF or 1,4-dioxane, whichproduced ThCl₄(H₂O)₄.(THF)₅ and ThCl₄(H₂O)₄.(1,4-dioxane)₃,respectively.

Me₃SiCl was used as a drying reagent for ThCl₄(H₂O)₄. Unfortunately,reaction between ThCl₄(H₂O)₄ and Me₃SiCl in THF resulted in THFpolymerization, which precluded the isolation of a thorium compound. Thesame reaction was performed in the presence of an excess of anhydrousHCl (2.0 M/diethyl ether). Under these conditions, the monohydratecomplex ThCl₄(H₂O)(THF)₃ formed rapidly; however, removal of theresidual H₂O results in THF polymerization. Replacing THF by DME as asolvent, however, resulted in successful dehydration of ThCl₄(H₂O)₄using Me₃SiCl (eqn (2)). The reaction is complete after 12 h at 90° C.and ThCl₄(DME)₂ is easily isolated in nearly quantitative yield (95%)after precipitation with hexane. ThCl₄(DME)₂ was characterized by acombination of ¹H and ¹³C{¹H} NMR spectroscopy, elemental analysis andX-ray crystallography.

Synthesis of ThCl₄(H₂O)₄A 500-mL round-bottom flask was charged with thorium nitrateTh(NO₃)₄(H₂O)₅ (20.0 g, 35.1 mmol) and a magnetic stir bar. The solidwas then dissolved in concentrated HCl (100 mL) with stirring. In awell-ventilated fume hood, the resulting solution was refluxed for 6 huntil no evolution of orange-colored gas was observed and the reactionmixture was colorless (Caution! Nitrogen oxides are toxic and hazardousgases). Volatiles were removed under reduced pressure to affordThCl₄(H₂O)₄ as a white solid (8.1 g, 18.1 mmol, 100%). ¹H NMR (THF-d₅,298 K): δ 7.17 (bs, v_(1/2)=47 Hz; H₂O). Anal. Calcd. for Cl₄H₈O₄Th(mol. wt. 445.91): C, 0.00; H, 1.81. Found: C, <0.2 (not detected); H,1.56.Synthesis of ThCl₄(DME)₂A 500-mL round-bottom Schlenk flask equipped with a magnetic stir barwas charged with ThCl₄(H₂O)₄ (15.5 g, 34.8 mmol). The solid wasdissolved in DME (100 mL) under an argon flow. Using an addition funnel,Me₃SiCl (70 mL, 557 mmol) was added dropwise at room temperature as thereaction is exothermic; upon addition, a crystalline white precipitateforms. The reaction vessel was sealed and the mixture was stirred for 12h in an 50° C. oil bath. The volume was then concentrated to 20 mL underreduced pressure, leaving a white suspension. The reaction vessel isbrought into a drybox. Addition of hexanes (50 mL), followed byfiltration over a coarse-porosity fritted filter and drying underreduced pressure afforded ThCl₄(DME)₂ as a white solid (18.3 g, 33.1mmol, 95%). ¹H NMR(C₆D₆, 298K): δ 3.76 (s, 6H; OCH₃), 3.33 ppm (s, 4H;OCH₂). ¹³C{¹H} NMR(C₆D₆, 298K): δ 73.6 (s), 65.8 ppm (s). Anal. Calcd.for C₈H₂₀Cl₄O₄Th (mol. wt. 554.09): C, 17.34; H, 3.64. Found: C, 17.38;H, 3.63.

Example 2

ThCl₄(DME)₂ proved to be an excellent synthetic precursor to a widerange of thorium(IV) halide, alkoxide, amide and organometalliccomplexes, as outlined in FIG. 1. Displacement of the DME ligands bymonodentate ligands such as triphenylphosphine oxide (O═PPh₃) orbidentate ligands such as N,N-tetramethylethylenediamine (TMEDA)resulted in the complexes ThCl₄(O═PPh₃)₃ and ThCl₄(TMEDA)₂.Transmetallation chemistry using excess bromotrimethylsilane (Me₃SiBr)smoothly converted ThCl₄(DME)₂ to ThBr₄(DME)₂. Salt metathesis between 4equiv. potassium 2,6-di-tert-butylphenoxide and ThCl₄(DME)₂quantitatively afforded the homoleptic alkoxide complexTh(O-2,6-^(t)Bu-C₆H₃)₄. Similarly, reaction of 4 equiv. sodiumhexamethyldisilazide with ThCl₄(DME)₂ yielded the known cyclometallated[(Me₃Si)₂N]₂Th[κ²-(C,N)—CH₂Si(CH₃)₂N(SiMe₃)] complex in approximately93% yield. Finally, the bis(pentamethylcyclopentadienyl) complex(C₅Me₅)₂ThCl₂ was prepared in approximately 88% yield from ThCl₄(DME)₂and 2 equiv. (C₅Me₅)MgCl.THF. Overall, the reaction chemistry withThCl₄(DME)₂ has been performed to produce multigram quantities in highyields (e.g., greater than 88%).

Synthesis of ThCl₄(0=PPh₃)₃

A 125-mL sidearm flask was charged with a magnetic stir bar, ThCl₄(DME)₂(1.40 g, 2.52 mmol), triphenylphosphine oxide (2.10 g, 7.55 mmol) andTHF (30 mL). The reaction mixture was stirred at room temperature for 6h. The volatiles were then removed under reduced pressure to giveThCl₄(O═PPh₃)₃ as a white solid (3.05 g, 2.52 mmol, 100%). ¹H NMR(THF-d₅, 298K): δ 7.83 (bs, 18H; Ph), 7.53 (bs, 9H; Ph), 7.43 (bs, 18H;Ph).Synthesis of ThCl₄(TMEDA)₂A 20-mL scintillation vial was charged with a stir bar, ThCl₄(DME)₂(0.280 g, 0.505 mmol) and THF (3 mL). To the resulting solution, TMEDA(100 μL, 0.667 mmol) was added using a syringe. The reaction mixture wasstirred at room temperature for 30 min. The volatiles were then removedunder reduced pressure to give ThCl₄(TMEDA)₂ as a white solid (0.306 g,0.505 mmol, 100%). The ¹H NMR spectrum collected in C₆D₆ was consistentwith the data previously reported for ThCl₄(TMEDA)₂.Synthesis of ThBr₄(DME)₂A 20-mL scintillation vial was charged with a stir bar, ThCl₄(DME)₂(0.280 g, 0.505 mmol) and toluene (3 mL). To the resulting solution,Me₃SiBr (330 μL, 2.50 mmol) was added using a syringe. The reactionmixture was stirred at room temperature for 48 h. The volatiles werethen removed under reduced pressure to give ThBr₄(DME)₂ as a white solid(0.369 g, 0.505 mmol, 100%). The ¹H NMR spectrum collected in C₆D₆ isconsistent with the data previously reported for complex ThBr₄(DME)₂.Synthesis of Th(O-2,6²Bu₂-C₆H₃)₄In a drybox, a 250-mL sidearm flask equipped with a stir bar was chargedwith ThCl₄(DME)₂ (5.30 g, 9.57 mmol) and THF (15 mL). A THF (100 mL)solution of potassium 2,6-di-tert-butylphenoxide (9.59 g, 39.2 mmol) wasadded dropwise at room temperature. The reaction mixture was stirred for3 h and then filtered through a Celite-padded coarse-porosity frittedfilter. The volatiles were removed under reduced pressure and theresulting off-white solid extracted into 100 mL hot (60° C.) toluene.The solution was collected and the volatile removed under reducedpressure to give Th(O-2,6-^(t)Bu₂-C₆H₃)₄ as a white solid (9.98 g, 9.47mmol, 99%). ¹H and ¹³C{¹H} NMR spectra collected in C₆D₆ were consistentwith the data previously reported for Th(O-2,6^(t)Bu₂-C₆H₃)₄.Synthesis of [(Me₃Si)₂N]₂Th[κ²-(N,C)—CH₂Si(CH₃)₂N(SiMe₃)]In a drybox, a 250-mL Schlenk flask equipped with a stir bar was chargedwith ThCl₄(DME)₂ (4.76 g, 86.0 mmol), Na[N(SiMe₃)₂] (6.30 g, 34.4 mmol)and toluene (100 mL). The reaction vessel was sealed, transferred to afume hood, and heated in a 110° C. oil bath for 24 h. The volatiles werethen removed under reduced pressure and the resulting white solid wasextracted with 60 mL hexane and filtered through a Celite-paddedcoarse-porosity flitted filter. The volume of the collected filtrate wasreduced to 10 mL and (Me₃Si)₂O (50 mL) was added. The resulting whitesuspension was cooled to −35° C., filtered using a fine-porosity frittedfilter, and dried under reduced pressure to give[(Me₃Si)₂N]₂Th[κ²-(N,C)—CH₂Si(CH₃)₂N(SiMe₃)] as a white solid (5.69 g,7.99 mmol, 93%). The ¹H NMR spectrum collected in C₆D₆ was consistentwith the data previously reported for[(Me₃Si)₂N]₂Th[κ²-(N,C)—CH₂Si(CH₃)₂N(SiMe₃)].Synthesis of (C₅Me₅)₂ThCl₂A 250-mL round-bottom Schlenk flask equipped with a magnetic stir barwas charged with ThCl₄(DME)₂ (5.37 g, 9.70 mmol), (C₅Me₅)MgCl.THF (5.70g, 21.3 mmol) and toluene (70 mL). The reaction vessel was sealed,transferred to a hood, and heated in an 100° C. oil bath for 48 h withstirring. The reaction mixture was cooled to ambient temperature andtransferred to a drybox. The solution was heated and filtered while hotthrough a Celite-padded coarse-porosity fitted filter. The solidcollected was washed with 15 mL hot (100° C.) toluene and dried underreduced pressure to give as a white solid (C₅Me₅)₂ThCl₂ (4.89 g, 8.54mmol, 88%). The ¹H NMR spectrum collected in C₆D₆ was consistent withthe data previously reported for (C₅Me₅)₂ThCl₂.

Example 3

Despite its great synthetic profile, the DME ligand in ThCl₄(DME)₂ isnot displaced by weak donor ligands such as THF. To prevent this frombeing an issue, other donors were examined as alternatives to DME. Theinsolubility of ThCl₄(H₂O)₄ in most organic solvents precluded itsreaction with Me₃SiCl. Although ThCl₄(H₂O)₄ is fairly soluble in1,4-dioxane, no reaction was observed with Me₃SiCl, even after severaldays at 150° C. However, addition of anhydrous HCl (2.0 M/diethyl ether)to the reaction medium leads to the quantitative formation of the novelthorium(IV) tetrachloride complex ThCl₄(1,4-dioxane)₂ after 12 h at 130°C. (eqn (3)). The insolubility of ThCl₄(1,4-dioxane)₂ innon-coordinating solvents did not permit its characterization using NMRspectroscopy; however, its identity as ThCl₄(1,4-dioxane)₂ was confirmedby elemental analysis. Although only poor quality crystallographic datacould be obtained for ThCl₄(1,4-dioxane)₂, connectivity was establishedand showed bridging 1,4-dioxane ligands, leading to the formation of anextended polymeric structure. This observation accounts for the apparentlow coordination number of 6 suggested by the stoichiometry inThCl₄(1,4-dioxane)₂.

In contrast to the DME ligands in ThCl₄(DME)₂, the 1,4-dioxane ligandsin ThCl₄(1,4-dioxane)₂ are easily displaced by THF, leading to the novelcomplex ThCl₄(THF)₃.5 (eqn (4)), which was fully characterized using ¹HNMR spectroscopy and elemental analysis. Whereas the dioxane adduct isstable in solution and in the solid state at 130° C., the THF adductThCl₄(THF)_(3.5) is thermally sensitive and eventually undergoes THFring-opening at room temperature. It is remarkable that this new routepermits access to the THF adduct, whereas direct synthesis fromThCl₄(H₂O)₄ systematically failed. This clearly establishes thesynthetic utility of the dioxane adduct. Both the dioxane and the THFadducts are easily converted to ThCl₄(DME)₂ by reaction with DME (eqn(5)).

Synthesis of ThCl₄(1,4-dioxane)₂In a drybox, a 20-mL thick-walled Schlenk tube equipped with a Teflonvalve and a stir bar was charged with ThCl₄(H₂O)₄ (1.30 g, 2.92 mmol).Next, 1,4-dioxane (4.0 mL), TMSCl (4.0 mL, 31.6 mmol) and a solution ofHCl/diethyl ether (4.0 mL, 2.0 M, 8.0 mmol) were added using a syringe.The reaction vessel was sealed and the reaction mixture stirred for 15 hin a 130° C. oil bath. The reaction mixture was then cooled to ambienttemperature and tranferred to a drybox. The solution was concentrated tohalf its original volume (˜6 mL) and hexane (15 mL) was added. Theresulting white suspension was collected over a fine-porosity frittedfilter and dried under reduced pressure to give ThCl₄(1,4-dioxane)₂ as awhite solid (1.57 g, 2.86 mmol, 98%). The insolubility ofThCl₄(1,4-dioxane)₂ in noncoordinating solvents precluded itscharacterization using NMR spectroscopy. Dissolution ofThCl₄(1,4-dioxane)₂ in coordinating solvents (such as THF) leads to thedisplacement of the 1,4-dioxane ligands. Anal. Calcd. for C₈H₁₆Cl₄O₄Th(mol. wt. 550.06): C, 17.47; H, 2.93; Cl, 25.78; Th, 42.18. Found: C,17.57; H, 2.63; Cl, 26.0; Th, 38.5.Synthesis of ThCl₄(THF)_(3.5)A 20-mL scintillation vial was charged with ThCl₄(1,4-dioxane)₂ (0.500g, 0.909 mmol) and THF (5 mL). The resulting solution was stirred atroom temperature for 10 minutes. The volatiles were removed underreduced pressure affording ThCl₄(THF)₃.5 as a white solid (0.569 g,0.909 mmol, 100%). ¹H NMR(C₆D₆, 298K): δ 3.98 (s, 4H; CH₂O), 1.28 ppm(s, 4H; CH₂CH₂O). Anal. Calcd. for C₁₄H₂₈Cl₄O₃₅Th (mol. wt. 626.22): C,26.85; H, 4.51; Cl, 22.65. Found: C, 27.03; H, 4.53; Cl, 23.0.

In all embodiments of the present invention, all percentages are byweight of the total composition, unless specifically stated otherwise.All ratios are weight ratios, unless specifically stated otherwise. Allranges are inclusive and combinable. All numerical amounts areunderstood to be modified by the word “about” unless otherwisespecifically indicated. All documents cited in the Detailed Descriptionof the Invention are, in relevant part, incorporated herein byreference; the citation of any document is not to be construed as anadmission that it is prior art with respect to the present invention. Tothe extent that any meaning or definition of a term in this documentconflicts with any meaning or definition of the same term in a documentincorporated by reference, the meaning or definition assigned to thatterm in this document shall govern.

Whereas particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A method of producing anhydrous thorium(IV)tetrahalide complexes comprising: a) providing Th(NO₃)₄(H₂O)_(x), wherex is at least 4; b) reacting said Th(NO₃)₄(H₂O)_(x)with ahalide-containing strong acid to produce ThX₄(H₂O)₄, wherein X is ahalide selected from the group consisting of bromide, chloride, iodide,and combinations thereof; and, c) drying the ThX₄(H₂O)₄ with Me₃SiCl ora mixture of anhydrous HC1 and Me₃SiCl in a suitable solvent to producea ThX₄-ligand complex of the formula ThX₄(ligand)₂, wherein a moleculeof ligand is a molecule of the suitable solvent, the suitable solventselected from the group consisting of dimethoxyethane and dioxane. 2.The method of claim 1, wherein X is chloride.
 3. The method of claim 1,wherein the solvent is dimethoxyethane.
 4. The method of claim 3,wherein the ThX₄-ligand complex is ThCl₄(dimethoxyethane)₂.
 5. Themethod of claim 1, wherein the solvent is a dioxane.
 6. The method ofclaim 5, wherein the ThX₄-ligand complex is ThCl₄(1,4-dioxane)₂.
 7. Themethod of claim 1, wherein the ThX₄-ligand complex is present in a yieldof at least 90%.
 8. The method of claim 1, wherein the reaction isperformed at a temperature of 130° C. or less.
 9. A compound having thestructure: